Method of fabricating an ink jet printhead chip with differential expansion actuators

ABSTRACT

A method of fabricating an inkjet printhead chip includes the step of forming a layer of sacrificial material on a substrate, such that the layer is between three and ten microns thick. A first layer of thermal expansion material is formed on the sacrificial material. A heater circuit is formed on the first layer of thermal expansion material. The sacrificial material and the first layer of thermal expansion material are formed to permit the electrical circuit to make electrical contact with the drive circuitry. A second layer of the thermal expansion material is formed on the heater circuit. A suitable process is applied on the second layer of thermal expansion material to render a surface of the second layer hydrophilic. The sacrificial material is removed.

[0001] This is a Continuation application on 10/693,948 filed on Oct.28, 2003

FIELD OF THE INVENTION

[0002] The present invention relates to ink jet printing. In particular,the invention relates to an ink-jet printhead chip having a plurality ofnozzle arrangements, each incorporating a substantially planar actuatorsand to a method of manufacturing such a printhead chip.

BACKGROUND OF THE INVENTION

[0003] Many different types of printing have been invented, a largenumber of which are presently in use. Known forms of printers have avariety of methods for marking the print media with a relevant markingmedia. Commonly used forms of printing include offset printing, laserprinting and copying devices, dot matrix type impact printers, thermalpaper printers, film recorders, thermal wax printers, dye sublimationprinters and ink jet printers both of the drop on demand and continuousflow type. Each type of printer has its own advantages and problems whenconsidering cost, speed, quality, reliability, simplicity ofconstruction and operation etc.

[0004] In recent years, the field of ink jet printing, wherein eachindividual pixel of ink is derived from one or more ink nozzles, hasbecome increasingly popular primarily due to its inexpensive andversatile nature.

[0005] Many different techniques of ink jet printing have been invented.For a survey of the field, reference is made to an article by J Moore,“Non-Impact Printing: Introduction and Historical Perspective”, OutputHard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).

[0006] Ink Jet printers themselves come in many different forms. Theutilization of a continuous stream of ink in ink jet printing appears todate back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hanselldiscloses a simple form of continuous stream electro-static ink jetprinting.

[0007] U.S. Pat. No. 3,596,275 by Sweet also discloses a process of acontinuous ink jet printing including the step wherein the ink jetstream is modulated by a high frequency electro-static field so as tocause drop separation. This technique is still utilized by severalmanufacturers including Elmjet and Scitex (see also U.S. Pat. No.3,373,437 by Sweet et al)

[0008] Piezoelectric ink jet printers are also one form of commonlyutilized ink jet printing device. Piezoelectric systems are disclosed byKyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes adiaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970)which discloses a squeeze mode of operation of a piezoelectric crystal,Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode ofpiezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 discloses apiezoelectric push mode actuation of the ink jet stream and Fischbeck inU.S. Pat. No. 4,584,590 which discloses a shear mode type ofpiezoelectric transducer element.

[0009] Recently, thermal ink jet printing has become an extremelypopular form of ink jet printing. The ink jet printing techniquesinclude those disclosed by Endo et al in GB 2007162 (1979) and Vaught etal in U.S. Pat. No. 4,490,728. Both the aforementioned referencesdisclose ink jet printing techniques that rely upon the activation of anelectrothermal actuator which results in the creation of a bubble in aconstricted space, such as a nozzle, which thereby causes the ejectionof ink from an aperture connected to the confined space onto a relevantprint media. Manufacturers such as Canon and Hewlett Packard manufactureprinting devices utilizing the electro-thermal actuator.

[0010] As can be seen from the foregoing, many different types ofprinting technologies are available. Ideally, a printing technologyshould have a number of desirable attributes. These include inexpensiveconstruction and operation, high-speed operation, safe and continuouslong-term operation etc. Each technology may have its own advantages anddisadvantages in the areas of cost, speed, quality, reliability, powerusage, simplicity of construction operation, durability and consumables.

[0011] In the parent application, U.S. Pat. No. 6,416,167, there isdisclosed a printing technology that is based on micro-electromechanicalsystems (MEMS) devices. In particular there is disclosed a printingmechanism that incorporates a MEMS device. There is also disclosed amethod of fabricating such a mechanism.

[0012] The fabrication of MEMS devices is based on integrated circuitfabrication techniques. Very generally, a sacrificial material isdeposited on a wafer substrate. A functional layer is then deposited onthe sacrificial material. The functional layer is patterned to form aMEMS component. The sacrificial layer is then removed to free the MEMScomponent.

[0013] Applicant has found that topography of a MEMS chip is veryimportant. The components are required to move. It follows that thetopography must be such that sufficient clearance is provided formovement of the components. This means that such features as nozzlechambers must be deep enough to provide for functional movement of anactuator positioned in the nozzle chamber.

[0014] There are, however, problems associated with deep topography.This problem is illustrated in Figures A and B of the drawings. InFigure A there is shown a substrate 1 with a layer of sacrificialmaterial 2 positioned on the substrate 1.

[0015] One problem is immediately apparent. It is extremely difficult toachieve a uniform deposition on side walls 2 and a floor 3 of the cavity4. The fluid dynamics of the deposition process is the primary reasonfor this. As a result, a portion of the sacrificial material within thecavity 4 tends to taper in to the side walls 2.

[0016] Accurate etching of the sacrificial material relies on a highimage focus on the layer 2. It will be appreciated that this focus couldbe lost in the cavity 4, due to the depth of the cavity 4. This resultsin poor etching within the cavity 4.

[0017] Etching is carried out using a device that etches in steps. Theseare usually 1 micron in depth. It follows that each stepping processremoves 1 micron of sacrificial material at a time. As can be seen inFigure B, once a required part of the layer 2 has been removed, a partis left behind in the cavity 4. This is called a stringer 5. It will beappreciated that the stringer 5 is difficult to remove and is thereforean undesirable result.

[0018] The Applicant has conceived the present invention to provide aprinthead chip that incorporates MEMS components that are spaced apredetermined distance from a wafer substrate so that sufficient inkejection can be achieved. The predetermined distance is such that thechip topography avoids the problems described above.

SUMMARY OF THE INVENTION

[0019] According to a first aspect of the invention, there is provided amethod of fabricating a printhead chip for an inkjet printhead, theprinthead chip including a wafer substrate that incorporates drivecircuitry and defines a plurality of ink inlet channels, a plurality ofnozzle arrangements positioned on the substrate, each nozzle arrangementincluding nozzle chamber walls that define a nozzle chamber and an inkejection port in fluid communication with the nozzle chamber with an inkinlet channel opening into the nozzle chamber and an actuator that ispositioned in the nozzle chamber, the actuator having an electricalcircuit connected to the drive circuitry layer and positioned in thermalexpansion material so that the expansion material experiencesdifferential thermal expansion and contraction when the heating circuitreceives an electrical signal from the drive circuitry layer and theactuator is displaced towards and away from the ink ejection port toeject a drop of ink from the nozzle chamber, the method comprising thesteps of:

[0020] forming a layer of sacrificial material on the substrate, suchthat the layer is between three and ten microns thick;

[0021] forming a first layer of the thermal expansion material on thesacrificial material;

[0022] forming the heater circuit on the first layer of thermalexpansion material, the sacrificial material and the first layer ofthermal expansion material being formed to permit the electrical circuitto make electrical contact with the drive circuitry;

[0023] forming a second layer of the thermal expansion material on theheater circuit;

[0024] applying a suitable process on the second layer of thermalexpansion material to render a surface of the second layer hydrophilic;and

[0025] removing the sacrificial material.

[0026] The layer of sacrificial material may be formed to be betweenthree and six microns thick.

[0027] The thermal expansion material and the heater circuit may beformed so that each actuator overlies a respective ink inlet opening.

[0028] The expansion material may be polytetrafluoroethylene (PTFE) andthe method may include the step of plasma processing the surface of thesecond layer of PTFE to render said surface hydrophilic.

[0029] The method may include the steps of forming a further layer ofsacrificial material on the second layer of PTFE, forming the nozzlechamber walls on the second layer of sacrificial material such that thenozzle chamber walls define the nozzle chamber and the ink ejection portin fluid communication with the nozzle chamber and removing the secondlayer of sacrificial material.

[0030] The method may include the step of forming the first and secondlayers of expansion material and the heater circuit such that theactuator is a laminated structure with the heater circuit sandwichedbetween the first and second layers of expansion material.

[0031] According to a second aspect of the invention, there is provideda printhead chip for an ink-jet printhead, the printhead chip comprising

[0032] a wafer substrate that incorporates drive circuitry, the wafersubstrate defining a plurality of ink inlet channels; and

[0033] nozzle arrangements positioned on the wafer substrate, eachnozzle arrangement comprising

[0034] a passive nozzle chamber structure that extends from the wafersubstrate and bounds a respective ink inlet channel;

[0035] a dynamic nozzle chamber structure that, together with thepassive structure, defines a nozzle chamber, and has a roof that definesthe ink ejection port, the dynamic structure being displaceable towardsthe wafer substrate into an actuated position and away from the wafersubstrate into a rest position such that a drop of ink can be ejectedfrom the ink ejection port, and

[0036] an elongate micro-electromechanical actuator connected betweenthe wafer substrate and the dynamic structure, the actuator including abeam assembly that has an active beam of a conductive material, capableof thermal expansion, that defines a heating circuit and is connected tothe drive circuitry and a passive beam that is interposed between theactive beam and the wafer substrate such that, when the active beamreceives an electrical signal from the drive circuitry, the active beamexpands relative to the passive beam driving the dynamic structure intothe actuated position to generate the drop of ink and when the signal iscut off subsequent cooling of the active beam causes the dynamicstructure to move back to the rest position, facilitating a separationof the drop of ink.

[0037] Each dynamic structure may include a skirt portion that dependsfrom the roof inwardly of the passive structure, such that an edge ofthe skirt portion is proximate an edge of the passive structure in therest position. The edges of the skirt portion and the passive structuremay be configured so that, when the nozzle chamber is filled with ink, ameniscus is defined between the edges. The meniscus may define a fluidicseal as the active structure is displaced between the actuated and restpositions.

[0038] The edge of each skirt portion may be positioned between threeand six microns above the wafer substrate, when the dynamic structure isin the rest position.

[0039] Each beam assembly may have an arm that interconnects the beamsand the dynamic structure, so that displacement of the active andpassive beams is transferred to the dynamic structure via the arm.

[0040] Each passive beam may be fixed, at one end, to the substrate, butinsulated from the drive circuitry and fixed at an opposed end to thearm. Each active beam may be fixed, at one end, to the substrate to beelectrically connected to the drive circuitry layer and also fixed at anopposed end to the arm.

[0041] Each passive beam and each passive structure may be of the samematerial.

[0042] According to a second aspect of the invention, there is providedan ink jet printhead chip that comprises

[0043] a wafer substrate,

[0044] a CMOS drive circuitry layer positioned on the wafer substrate,and

[0045] a plurality of nozzle arrangements positioned on the wafersubstrate and the CMOS drive circuitry layer, each nozzle arrangementcomprising

[0046] nozzle chamber walls and a roof wall that define a nozzle chamberand an ink ejection port defined in the roof wall, and

[0047] a micro-electromechanical actuator connected to the CMOS drivecircuitry layer and that has at least one movable member that ispositioned to act on ink in the nozzle chamber to eject the ink from theink ejection port on receipt of a signal from the drive circuitry layer,the, or each, movable member being spaced between 2 microns and 15microns from the CMOS drive circuitry layer.

[0048] The at least one movable member of each nozzle arrangement may bespaced between 5 microns and 12 microns from the CMOS drive circuitrylayer. More particularly, the at least one movable member of each nozzlearrangement may be spaced between 6 microns and 10 microns from the CMOSdrive circuitry layer.

[0049] The nozzle chamber walls and roof walls of each nozzlearrangement may be configured so that the nozzle chambers are generallyrectangular in plan and transverse cross section. Each movable membermay be planar and rectangular to extend across a length of itsrespective nozzle chamber. A free end of the movable member may bepositioned between the CMOS drive circuitry layer and the ink ejectionport. An opposed end of the movable member may be anchored to the CMOSdrive circuitry layer. The movable member may incorporate heatingcircuitry that is electrically connected to the CMOS drive circuitrylayer. The movable member may be configured so that, when the heatingcircuitry receives a signal from the CMOS drive circuitry layer, themovable member is displaced towards the ink ejection port as a result ofdifferential expansion and, when the signal is terminated, the movablemember is displaced away from the ink ejection port as a result ofdifferential contraction.

[0050] Instead, the movable member may include an actuator arm of aconductive material that is configured to define a heating circuit thatis connected to the CMOS drive circuitry layer and is configured todeflect towards the wafer substrate as a result of differentialexpansion when an electrical signal is received from the CMOS drivecircuitry layer. The roof wall of the nozzle chamber and at least partof the nozzle chamber walls may be connected to the actuator arm, sothat, when the actuator arm is deflected towards the wafer substrate,ink is ejected from the ink ejection port defined in the roof wall.

[0051] The invention extends to an ink jet printhead chip that includesa plurality of printhead chips as described above.

[0052] According to a third aspect of the invention, there is provided amethod of fabricating an ink jet printhead chip having a wafersubstrate, a CMOS drive circuitry layer positioned on the wafersubstrate and a plurality of nozzle arrangements positioned on the wafersubstrate and the CMOS drive circuitry layer, each nozzle arrangementhaving nozzle chamber walls and a roof wall that define a nozzle chamberand an ink ejection port in the roof wall and a micro-electromechanicalactuator connected to the CMOS drive circuitry layer the actuator havingat least one movable member that is positioned to act on ink in thenozzle chamber to eject the ink from the ink ejection port on receipt ofa signal from the drive circuitry layer, the method comprising the stepsof:

[0053] depositing between 2 microns and 15 microns of a firstsacrificial material on the CMOS drive circuitry layer to define adeposition area for a layer of actuator material,

[0054] depositing said layer of actuator material on said depositionarea,

[0055] etching the layer of actuator material to form at least part ofeach micro-electromechanical actuator, and

[0056] forming the nozzle chamber walls and roof wall by at least one ofa deposition and an etching process.

[0057] The method may include the step of depositing between 5 micronsand 12 microns of the first sacrificial material on the CMOS drivecircuitry layer. In particular, the method may include the step ofdepositing between 6 and 10 microns of the first sacrificial material onthe CMOS drive circuitry layer.

[0058] The step of forming the nozzle chamber walls and roof wall ofeach nozzle arrangement may include the steps of:

[0059] depositing a second sacrificial material on the layer of actuatormaterial to define a deposit area for at least part of the nozzlechamber walls and the roof wall,

[0060] depositing a structural material on the deposit area, and

[0061] etching the structural material to form the at least part of thenozzle chamber walls and the roof wall.

BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Notwithstanding any other forms, which may fall within the scopeof the present invention, preferred forms of the invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings in which:

[0063] Fig. A is a schematic diagram indicating problems associated withdeep topography in a printhead chip, as set out in the background of theinvention.

[0064] Fig. B is a schematic diagram indicating problems associated withdeep topography in a printhead chip, as set out in the background of theinvention.

[0065]FIGS. 1-3 illustrate basic operation of the preferred embodimentsof nozzle arrangements of a printhead chip of the invention.

[0066]FIG. 4 is a sectional view of one embodiment of a nozzlearrangement of a printhead chip of the invention.

[0067]FIG. 5 is an exploded perspective view of the nozzle arrangementof FIG. 4.

[0068]FIGS. 6-15 are cross-sectional views of the printhead chip of theinvention illustrating successive steps in the fabrication of theprinthead chip according to a method of the invention.

[0069]FIG. 16 illustrates a top view of the printhead chip of theinvention.

[0070]FIG. 17 is a legend of the materials used in a method of theinvention described with reference to FIGS. 18 to 29.

[0071]FIG. 18 to FIG. 29 illustrate sectional views of the manufacturingsteps in one form of construction of an ink jet printhead having nozzlearrangements of the invention.

[0072]FIG. 30 shows a three dimensional, schematic view of a nozzlearrangement for an ink jet printhead in accordance with anotherembodiment of the invention.

[0073] FIGS. 31 to 33 show a three dimensional, schematic illustrationof an operation of the nozzle arrangement of FIG. 30.

[0074]FIG. 34 shows a three dimensional view of another ink jetprinthead chip according to the invention.

[0075]FIG. 35 shows, on an enlarged scale, part of the ink jet printheadchip of FIG. 34.

[0076]FIG. 36 shows a three dimensional view of the ink jet printheadchip with a nozzle guard.

[0077]FIGS. 37a to 37 r show three-dimensional views of steps in thefabrication of a nozzle arrangement of the ink jet printhead chip.

[0078]FIGS. 38a to 38 r show sectional side views of the fabricationsteps of FIGS. 37a to 37 r.

[0079]FIGS. 39a to 39 k show layouts of masks used in various steps inthe fabrication process.

[0080]FIGS. 40a to 40 c show three-dimensional views of an operation ofthe nozzle arrangement fabricated according to the method of FIGS. 37and 38.

[0081]FIGS. 41a to 41 c show sectional side views of an operation of thenozzle arrangement fabricated according to the method of FIGS. 37 and38.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

[0082] In the preferred embodiments of the invention, a drop on demandink jet nozzle arrangement is provided which allows for the ejection ofink on demand by means of a thermal actuator which operates to eject theink from a nozzle chamber. The nozzle chamber is formed directly over anink supply channel thereby allowing for an extremely compact form ofnozzle arrangement. The extremely compact form of nozzle arrangementallows for minimal area to be taken up by a printing mechanism therebyresulting in improved economics of fabrication.

[0083] Turning initially to FIGS. 1-3, the operation of the preferredembodiment of the nozzle arrangement is now described. In FIG. 1, thereis illustrated a sectional view of two ink jet nozzle arrangements 10,11 which are formed on a silicon wafer 12 which includes a series ofthrough-wafer ink supply channels 13.

[0084] Located over a portion of the wafer 12 and over the ink supplychannel 13 is a thermal actuator 14, which is actuated so as to ejectink from a corresponding nozzle chamber. The actuator 14 is placedsubstantially over the ink supply channel 13. In the quiescent position,the ink fills the nozzle chamber and an ink meniscus 15 forms across anink ejection port 35 of the chamber.

[0085] The actuator 14 is spaced between 6 microns and 10 microns abovethe wafer 12.

[0086] When it is desired to eject a drop from the chamber, the thermalactuator 14 is activated by passing a current through the actuator 14.The actuation causes the actuator 14 to rapidly bend upwards asindicated in FIG. 2. The movement of the actuator 14 results in anincrease in the ink pressure around an ejection port 35 (FIG. 4) of thechamber, which in turn causes, a significant bulging of the meniscus 15and a flow of ink out of the nozzle chamber. The actuator 14 can beconstructed so as to impart sufficient momentum to the ink to cause thedirect ejection of a drop.

[0087] As indicated in FIG. 3, the activation of actuator 14 can betimed so as to turn the actuation current off at a predetermined point.This causes the return of the actuator 14 to its original positionthereby resulting in a consequential backflow of ink in the direction ofan arrow 17 into the chamber. A body of ink 18 necks and separates andcontinues towards output media, such as paper, for printing. Theactuator 14 then returns to its quiescent position and surface tensioneffects result in a refilling of the nozzle chamber via the ink supplychannel 13 as a consequence of surface tension effects on the meniscus15. In time, the condition of the ink returns to that depicted in FIG.1.

[0088] In FIGS. 4 and 5, there is illustrated the structure of a singlenozzle arrangement 10 in more detail. FIG. 4 is a part sectional viewwhile FIG. 5 shows a corresponding exploded perspective view.

[0089] Many ink jet nozzle arrangements are formed at a time, on aselected wafer base 12 utilizing standard semi-conductor processingtechniques in addition to micro-machining and micro-fabrication processtechnology further details of this form of fabrication are set out infurther detail further on in this specification.

[0090] A CMOS drive circuitry layer 20 is formed on the wafer 12. TheCMOS layer 20 can, in accordance with standard techniques, includemulti-level metal layers sandwiched between oxide layers and preferablyat least a two level metal process is utilized. In order to reduce thenumber of necessary processing steps, the masks utilized include areasthat provide for a build up of an aluminum barrier 21 which can beconstructed from a first level 22 of aluminum and second level 23 ofaluminum. Additionally, aluminum portions 24 are provided which defineelectrical contacts to a subsequent heater layer. The aluminum barrier21 is important for providing an effective barrier to the possiblesubsequent etching of the oxide within the CMOS layer 20 when asacrificial etchant is utilized in the construction of the nozzlearrangement 10 with the etchable material preferably being glass layers.

[0091] A nitride passivation layer 26 is formed on the CMOS layer 20 toprotect the lower CMOS layers from sacrificial etchants and ink erosion.Above the nitride layer 26 there is formed a gap 28 in which an airbubble forms during operation. The gap 28 can be constructed by layingdown a sacrificial layer and subsequently etching the gap 28 as will beexplained hereinafter. The air gap 28 is between 6 microns and 10microns thick.

[0092] On top of the air gap 28 is constructed a polytetrafluoroethylene(PTFE) layer 29 which comprises a gold serpentine heater layer 30sandwiched between two PTFE layers. The gold heater layer 30 isconstructed in a serpentine form to allow it to expand on heating. Theheater layer 30 and PTFE layer 29 together comprise the thermal actuator14 of FIG. 1.

[0093] The outer PTFE layer 29 has an extremely high coefficient ofthermal expansion (approximately 770×10⁻⁶, or around 380 times that ofsilicon). The PTFE layer 29 is also normally highly hydrophobic whichresults in an air bubble being formed under the actuator in the gap 28due to out-gassing etc. The top PTFE surface layer is treated so as tomake it hydrophilic in addition to those areas around the ink supplychannel 13. This can be achieved with a plasma etch in an ammoniaatmosphere. The heater layer 30 is also formed within the lower portionof the PTFE layer.

[0094] The heater layer 30 is connected at ends e.g. 31 to the lowerCMOS drive layer 20 that contains the drive circuitry (not shown). Foroperation of the actuator 14, a current is passed through the goldheater element 30 that heats the bottom surface of the actuator 14. Thebottom surface of actuator 14, in contact with the air bubble remainsheated while any top surface heating is carried away by the exposure ofthe top surface of actuator 14 to the ink within a chamber 32. Hence,the bottom PTFE layer expands more rapidly resulting in a general rapidupward bending of actuator 14 (as illustrated in FIG. 2) thatconsequentially causes the ejection of ink from the ink ejection port35.

[0095] Turning off the current to the heater layer 30 can deactivate theactuator 14. This will result in a return of the actuator 14 to its restposition.

[0096] On top of the actuator 14 are formed nitride side wall portions33 and a top wall portion 34. The wall portions 33 and the top portions34 can be formed via a dual damascene process utilizing a sacrificiallayer. The top wall portion 34 is etched to define the ink ejection port35 in addition to a series of etchant holes 36 which are of a relativelysmall diameter and allow for effective etching of lower sacrificiallayers when utilizing a sacrificial etchant. The etchant holes 36 aremade small enough such that surface tension effects restrict thepossibilities of ink being ejected from the chamber 32 via the etchantholes 36 rather than the ejection port 35.

[0097] The various steps involved in the construction of an array of inkjet nozzle arrangements are explained in FIGS. 6 to 15.

[0098] 1. Turning initially to FIG. 6, the starting position comprises asilicon wafer 12 including a CMOS layer 20 which has nitride passivationlayer 26 and which is surface finished with a chemical—mechanicalplanarization process.

[0099] 2. The nitride layer is masked and etched as illustrated in FIG.7 so as to define portions of the nozzle arrangement and areas forinterconnection between any subsequent heater layer and a lower CMOSlayer.

[0100] 3. Next, a sacrificial oxide layer is deposited, masked andetched as indicated in FIG. 8 with the oxide layer being etched in thoseareas where a subsequent heater layer electronically contacts the lowerlayers.

[0101] 4. As illustrated in FIG. 9, a 1 micron layer of PTFE isdeposited and first masked and etched for the heater contacts to thelower CMOS layer and then masked and etched for the heater shape.

[0102] 5. Next, as illustrated in FIG. 10, the gold heater layer 30, 31is deposited. Due to the fact that it is difficult to etch gold, thelayer can be conformally deposited and subsequently portions removedutilizing chemical mechanical planarization so as to leave thoseportions associated with the heater element. The processing steps 4 and5 basically comprise a dual damascene process.

[0103] 6. Next, a top PTFE layer is deposited and masked and etched downto the sacrificial layer as illustrated in FIG. 11 so as to define theheater shape. Subsequently, the surface of the PTFE layer is plasmaprocessed so as to make it hydrophilic. Suitable processing can excludeplasma damage in an ammonia atmosphere. Alternatively, the surface couldbe coated with a hydrophilic material.

[0104] 7. A further sacrificial layer is then deposited and etched asillustrated in FIG. 12 so as to form the structure for the nozzlechamber. The sacrificial layer is then masked and etched in order todefine a deposition area for the nozzle chamber walls.

[0105] 8. As illustrated in FIG. 13, the nozzle chamber is formed byconformally depositing three microns of nitride and etching a masknozzle rim to a depth of one micron for the nozzle rim (the etched depthnot being overly time critical). Subsequently, a mask is utilized toetch the ink ejection port 35 in addition to the sacrificial layeretchant holes 36.

[0106] 9. As illustrated in FIG. 14, the backside of the wafer is maskedfor the ink channels and plasma etched through the wafer. A suitableplasma etching process can include a deep anisotropic trench etchingsystem such as that available from SDS Systems Limited (See) “AdvancedSilicon Etching Using High Density Plasmas” by J. K. Bhardwaj, H.Ashraf, page 224 of Volume 2639 of the SPIE Proceedings in MicroMachining and Micro Fabrication Process Technology).

[0107] 10. As illustrated in FIG. 15, the sacrificial layers are etchedaway utilizing a sacrificial etchant such as hydrochloric acid.Subsequently, the portion underneath the actuator that is around the inkchannel is plasma processed through the backside of the wafer to makethe panel end hydrophilic.

[0108] Subsequently, the wafer can be separated into separate printheadsand each printhead is bonded into an injection molded ink supply channeland the electrical signals to the chip can be tape automated bonded(TAB) to the printhead for subsequent testing. FIG. 16 illustrates a topview of nozzle arrangement constructed on a wafer so as to provide forpagewidth multicolor output.

[0109] One form of detailed manufacturing process that can be used tofabricate monolithic ink jet printheads operating in accordance with theprinciples taught by the present embodiment can proceed utilizing thefollowing steps:

[0110] 1. Using a double sided polished wafer, Complete drivetransistors, data distribution, and timing circuits using a 0.5 micron,one poly, 2 metal CMOS process. This step is shown in FIG. 18. Forclarity, these diagrams may not be to scale, and may not represent across section though any single plane of the nozzle. FIG. 17 is a key torepresentations of various materials in these manufacturing diagrams,and those of other cross-referenced ink jet configurations.

[0111] 2. Deposit 1 micron of low stress nitride. This acts as a barrierto prevent ink diffusion through the silicon dioxide of the chipsurface.

[0112] 3. Deposit 3 microns of sacrificial material (e.g. polyimide).

[0113] 4. Etch the sacrificial layer using Mask 1. This mask defines theactuator anchor point. This step is shown in FIG. 19.

[0114] 5. Deposit 0.5 microns of PTFE.

[0115] 6. Etch the PTFE, nitride, and CMOS passivation down to secondlevel metal using Mask 2. This mask defines the heater vias. This stepis shown in FIG. 20.

[0116] 7. Deposit and pattern resist using Mask 3. This mask defines theheater.

[0117] 8. Deposit 0.5 microns of gold (or other heater material with alow Young's modulus) and strip the resist. Steps 7 and 8 form a lift-offprocess. This step is shown in FIG. 21.

[0118] 9. Deposit 1.5 microns of PTFE.

[0119] 10. Etch the PTFE down to the sacrificial layer using Mask 4.This mask defines the actuator and the bond pads. This step is shown inFIG. 22.

[0120] 11. Wafer probe. All electrical connections are complete at thispoint, and the chips are not yet separated.

[0121] 12. Plasma process the PTFE to make the top and side surfaces ofthe actuator hydrophilic. This allows the nozzle chamber to fill bycapillarity.

[0122] 13. Deposit 10 microns of sacrificial material.

[0123] 14. Etch the sacrificial material down to nitride using Mask 5.This mask defines the nozzle chamber. This step is shown in FIG. 23.

[0124] 15. Deposit 3 microns of PECVD glass. This step is shown in FIG.24.

[0125] 16. Etch to a depth of 1 micron using Mask 6. This mask defines arim of the ejection port. This step is shown in FIG. 25.

[0126] 17. Etch down to the sacrificial layer using Mask 7. This maskdefines the ink ejection port and the sacrificial etch access holes.This step is shown in FIG. 26.

[0127] 18. Back-etch completely through the silicon wafer (with, forexample, an ASE Advanced Silicon Etcher from Surface Technology Systems)using Mask 8. This mask defines the ink inlets that are etched throughthe wafer. The wafer is also diced by this etch. This step is shown inFIG. 27.

[0128] 19. Back-etch the CMOS oxide layers and subsequently depositednitride layers and sacrificial layer through to PTFE using theback-etched silicon as a mask.

[0129] 20. Plasma process the PTFE through the back-etched holes to makethe top surface of the actuator hydrophilic. This allows the nozzlechamber to fill by capillarity, but maintains a hydrophobic surfaceunderneath the actuator. This hydrophobic section causes an air bubbleto be trapped under the actuator when the nozzle is filled with awater-based ink. This bubble serves two purposes: to increase theefficiency of the heater by decreasing thermal conduction away from theheated side of the PTFE, and to reduce the negative pressure on the backof the actuator.

[0130] 21. Etch the sacrificial material. The nozzle arrangements arecleared, the actuators freed, and the chips are separated by this etch.This step is shown in FIG. 28.

[0131] 22. Mount the printheads in their packaging, which may be amolded plastic former incorporating ink channels that supply theappropriate color ink to the ink inlets at the back of the wafer.

[0132] 23. Connect the printheads to their interconnect systems. For alow profile connection with minimum disruption of airflow, TAB may beused. Wire bonding may also be used if the printer is to be operatedwith sufficient clearance to the paper.

[0133] 24. Hydrophobize the front surface of the printheads.

[0134] 25. Fill the completed printheads with ink and test them. Afilled nozzle is shown in FIG. 29.

[0135] In FIG. 30 of the drawings, a nozzle arrangement, in accordancewith a further embodiment of the invention, is designated generally bythe reference numeral 110. An ink jet printhead chip of the inventionhas a plurality of nozzle arrangements 110 arranged in an array 114(FIGS. 34 and 35) on a silicon substrate 116. The array 114 will bedescribed in greater detail below.

[0136] The arrangement 110 includes a silicon substrate or wafer 116 onwhich a dielectric layer 118 is deposited. A CMOS passivation layer 120is deposited on the dielectric layer 118.

[0137] Each nozzle arrangement 110 includes a nozzle 122 defining anozzle opening 124, a connecting member in the form of a lever arm 126and an actuator 128. The lever arm 126 connects the actuator 128 to thenozzle 122.

[0138] As shown in greater detail in FIGS. 31 to 33 of the drawings, thenozzle 122 comprises a crown portion 130 with a skirt portion 132depending from the crown portion 130. The skirt portion 132 forms partof a peripheral wall of a nozzle chamber 134 (FIGS. 31 to 33 of thedrawings). The nozzle opening 124 is in fluid communication with thenozzle chamber 134. It is to be noted that the nozzle opening 124 issurrounded by a raised rim 136 that “p ins” a meniscus 138 (FIG. 31) ofa body of ink 140 in the nozzle chamber 134.

[0139] The skirt portion 132 is positioned between 6 microns and 10microns above the CMOS passivation layer 120.

[0140] An ink inlet aperture 142 (shown most clearly in FIG. 35 of thedrawing) is defined in a floor 146 of the nozzle chamber 134. Theaperture 142 is in fluid communication with an ink inlet channel 148defined through the substrate 116.

[0141] A wall portion 150 bounds the aperture 142 and extends upwardlyfrom the floor portion 146. The skirt portion 132, as indicated above,of the nozzle 122 defines a first part of a peripheral wall of thenozzle chamber 134 and the wall portion 150 defines a second part of theperipheral wall of the nozzle chamber 134.

[0142] The wall 150 has an inwardly directed lip 152 at its free endthat serves as a fluidic seal that inhibits the escape of ink when thenozzle 122 is displaced, as will be described in greater detail below.It will be appreciated that, due to the viscosity of the ink 140 and thesmall dimensions of the spacing between the lip 152 and the skirtportion 132, the inwardly directed lip 152 and surface tension functionas a seal for inhibiting the escape of ink from the nozzle chamber 134.

[0143] The actuator 128 is a thermal bend actuator and is connected toan anchor 154 extending upwardly from the substrate 116 or, moreparticularly, from the CMOS passivation layer 120. The anchor 154 ismounted on conductive pads 156 which form an electrical connection withthe actuator 128.

[0144] The actuator 128 comprises a first, active beam 158 arrangedabove a second, passive beam 160. In a preferred embodiment, both beams158 and 160 are of, or include, a conductive ceramic material such astitanium nitride (TiN).

[0145] Both beams 158 and 160 have their first ends anchored to theanchor 154 and their opposed ends connected to the arm 126. When acurrent is caused to flow through the active beam 158 thermal expansionof the beam 158 results. As the passive beam 160, through which there isno current flow, does not expand at the same rate, a bending moment iscreated causing the arm 126 and, hence, the nozzle 122 to be displaceddownwardly towards the substrate 116 as shown in FIG. 32 of thedrawings. This causes an ejection of ink through the nozzle opening 124as shown at 162 in FIG. 32 of the drawings. When the source of heat isremoved from the active beam 158, i.e. by stopping current flow, thenozzle 122 returns to its quiescent position as shown in FIG. 33 of thedrawings.

[0146] When the nozzle 122 returns to its quiescent position, an inkdroplet 164 is formed as a result of the breaking of an ink droplet neckas illustrated at 166 in FIG. 33 of the drawings. The ink droplet 164then travels on to the print media such as a sheet of paper. As a resultof the formation of the ink droplet 164, a “negative” meniscus is formedas shown at 168 in FIG. 33 of the drawings. This “negative” meniscus 168results in an inflow of ink 140 into the nozzle chamber 134 such that anew meniscus 138 (FIG. 31) is formed in readiness for the next ink dropejection from the nozzle arrangement 110.

[0147] Referring now to FIGS. 34 and 35 of the drawings, the nozzlearray 114 is described in greater detail. The array 114 is for afour-color printhead. Accordingly, the array 114 includes four groups170 of nozzle arrangements, one for each color. Each group 170 has itsnozzle arrangements 110 arranged in two rows 172 and 174. One of thegroups 170 is shown in greater detail in FIG. 35 of the drawings.

[0148] To facilitate close packing of the nozzle arrangements 110 in therows 172 and 174, the nozzle arrangements 110 in the row 174 are offsetor staggered with respect to the nozzle arrangements 110 in the row 172.Also, the nozzle arrangements 110 in the row 172 are spaced apartsufficiently far from each other to enable the lever arms 126 of thenozzle arrangements 110 in the row 174 to pass between adjacent nozzles122 of the arrangements 110 in the row 172. It is to be noted that eachnozzle arrangement 110 is substantially dumbbell shaped so that thenozzles 122 in the row 172 nest between the nozzles 122 and theactuators 128 of adjacent nozzle arrangements 110 in the row 174.

[0149] Further, to facilitate close packing of the nozzles 122 in therows 172 and 174, each nozzle 122 is substantially hexagonally shaped.

[0150] It will be appreciated by those skilled in the art that, when thenozzles 122 are displaced towards the substrate 116, in use, due to thenozzle opening 124 being at a slight angle with respect to the nozzlechamber 134 ink is ejected slightly off the perpendicular. It is anadvantage of the arrangement shown in FIGS. 34 and 35 of the drawingsthat the actuators 128 of the nozzle arrangements 110 in the rows 172and 174 extend in the same direction to one side of the rows 172 and174. Hence, the ink droplets ejected from the nozzles 122 in the row 172and the ink droplets ejected from the nozzles 122 in the row 174 areparallel to one another resulting in an improved print quality.

[0151] Also, as shown in FIG. 34 of the drawings, the substrate 116 hasbond pads 176 arranged thereon which provide the electrical connections,via the pads 156, to the actuators 128 of the nozzle arrangements 110.These electrical connections are formed via the CMOS layer (not shown).

[0152] Referring to FIG. 36 of the drawings, a development of theinvention is shown. With reference to the previous drawings, likereference numerals refer to like parts, unless otherwise specified.

[0153] In this development, a nozzle guard 180 is mounted on thesubstrate 116 of the array 114. The nozzle guard 180 includes a bodymember 182 having a plurality of passages 184 defined therethrough. Thepassages 184 are in register with the nozzle openings 124 of the nozzlearrangements 110 of the array 114 such that, when ink is ejected fromany one of the nozzle openings 124, the ink passes through theassociated passage 184 before striking the print media.

[0154] The body member 182 is mounted in spaced relationship relative tothe nozzle arrangements 110 by limbs or struts 186. One of the struts186 has air inlet openings 188 defined therein.

[0155] In use, when the array 114 is in operation, air is chargedthrough the inlet openings 188 to be forced through the passages 184together with ink travelling through the passages 184.

[0156] The ink is not entrained in the air as the air is charged throughthe passages 184 at a different velocity from that of the ink droplets164. For example, the ink droplets 164 are ejected from the nozzles 122at a velocity of approximately 3 m/s. The air is charged through thepassages 184 at a velocity of approximately 1 m/s.

[0157] The purpose of the air is to maintain the passages 184 clear offoreign particles. A danger exists that these foreign particles, such asdust particles, could fall onto the nozzle arrangements 110 adverselyaffecting their operation. With the provision of the air inlet openings88 in the nozzle guard 180 this problem is, to a large extent, obviated.

[0158] The nozzle arrangements 110 are configured to define a relativelyflat topography for the printhead chip. This is emphasized by the factthat the skirt portion 132 of each nozzle arrangement is between 6microns and 10 microns from the ink passivation layer 120. The problemsassociated with having deep topography are set out in the Background tothe Invention above. It follows that a particular advantage of theconfiguration of the nozzle arrangements 110 is that these problems areaddressed.

[0159] Referring now to FIGS. 37 to 39 of the drawings, a process formanufacturing the nozzle arrangements 110 is described.

[0160] Starting with the silicon substrate or wafer 116, the dielectriclayer 118 is deposited on a surface of the wafer 116. The dielectriclayer 118 is in the form of approximately 1.5 microns of CVD oxide.Resist is spun on to the layer 118 and the layer 118 is exposed to mask200 and is subsequently developed.

[0161] After being developed, the layer 118 is plasma etched down to thesilicon layer 116. The resist is then stripped and the layer 118 iscleaned. This step defines the ink inlet aperture 142.

[0162] In FIG. 37b of the drawings, approximately 0.8 microns ofaluminum 202 is deposited on the layer 118. Resist is spun on and thealuminum 202 is exposed to mask 204 and developed. The aluminum 202 isplasma etched down to the oxide layer 118, the resist is stripped andthe device is cleaned. This step provides the bond pads andinterconnects to the ink jet actuator 128. This interconnect is to anNMOS drive transistor and a power plane with connections made in theCMOS layer (not shown).

[0163] Approximately 0.5 microns of PECVD nitride is deposited as theCMOS passivation layer 120. Resist is spun on and the layer 120 isexposed to mask 206 whereafter it is developed. After development, thenitride is plasma etched down to the aluminum layer 202 and the siliconlayer 116 in the region of the inlet aperture 142. The resist isstripped and the device cleaned.

[0164] A layer 208 of a sacrificial material is spun on to the layer120. The layer 208 is 6 microns of photosensitive polyimide orapproximately 4 μm of high temperature resist. The layer 208 issoftbaked and is then exposed to mask 210 whereafter it is developed.The layer 208 is then hardbaked at 400° C. for one hour where the layer208 is comprised of polyimide or at greater than 300° C. where the layer208 is high temperature resist. It is to be noted in the drawings thatthe pattern-dependent distortion of the polyimide layer 208 caused byshrinkage is taken into account in the design of the mask 210.

[0165] In the next step, shown in FIG. 37e of the drawings, a secondsacrificial layer 212 is applied. The layer 212 is either 2 μm ofphotosensitive polyimide, which is spun on, or approximately 1.3 μm ofhigh temperature resist. The layer 212 is softbaked and exposed to mask214. After exposure to the mask 214, the layer 212 is developed. In thecase of the layer 212 being polyimide, the layer 212 is hardbaked at400° C. for approximately one hour. Where the layer 212 is resist, it ishardbaked at greater than 300° C. for approximately one hour.

[0166] A 0.2-micron multi-layer metal layer 216 is then deposited. Partof this layer 216 forms the passive beam 160 of the actuator 128.

[0167] It is to be noted that at this stage, there is between 5.3microns and 8 microns of sacrificial material forming a deposit area forthe passive beam 160 of the actuator 128.

[0168] The layer 216 is formed by sputtering 1,000 Å of titanium nitride(TiN) at around 300° C. followed by sputtering 50 Å of tantalum nitride(TaN). A further 1,000 Å of TiN is sputtered on followed by 50 Å of TaNand a further 1,000 Å of TiN.

[0169] Other materials that can be used instead of TiN are TiB₂, MoSi₂or (Ti, Al)N.

[0170] The layer 216 is then exposed to mask 218, developed and plasmaetched down to the layer 212 whereafter resist, applied for the layer216, is wet stripped taking care not to remove the cured layers 208 or212.

[0171] A third sacrificial layer 220 is applied by spinning on 4 μm ofphotosensitive polyimide or approximately 2.6 μm high temperatureresist. The layer 220 is softbaked whereafter it is exposed to mask 222.The exposed layer is then developed followed by hardbaking. In the caseof polyimide, the layer 220 is hardbaked at 400° C. for approximatelyone hour or at greater than 300° C. where the layer 220 comprisesresist.

[0172] A second multi-layer metal layer 224 is applied to the layer 220.The constituents of the layer 224 are the same as the layer 216 and areapplied in the same manner. It will be appreciated that both layers 216and 224 are electrically conductive layers.

[0173] The layer 224 is exposed to mask 226 and is then developed. Thelayer 224 is plasma etched down to the polyimide or resist layer 220whereafter resist applied for the layer 224 is wet stripped taking carenot to remove the cured layers 208, 212 or 220. It will be noted thatthe remaining part of the layer 224 defines the active beam 158 of theactuator 128.

[0174] A fourth sacrificial layer 228 is applied by spinning on 4 μm ofphotosensitive polyimide or approximately 2.6 μm of high temperatureresist. The layer 228 is softbaked, exposed to the mask 230 and is thendeveloped to leave the island portions as shown in FIG. 9k of thedrawings. The remaining portions of the layer 228 are hardbaked at 400°C. for approximately one hour in the case of polyimide or at greaterthan 300° C. for resist.

[0175] As shown in FIG. 371 of the drawing a high Young's modulusdielectric layer 232 is deposited. The layer 232 is constituted byapproximately 1 μm of silicon nitride or aluminum oxide. The layer 232is deposited at a temperature below the hardbaked temperature of thesacrificial layers 208, 212, 220, 228. The primary characteristicsrequired for this dielectric layer 232 are a high elastic modulus,chemical inertness and good adhesion to TiN.

[0176] A fifth sacrificial layer 234 is applied by spinning on 2 μm ofphotosensitive polyimide or approximately 1.3 μm of high temperatureresist. The layer 234 is softbaked, exposed to mask 236 and developed.The remaining portion of the layer 234 is then hardbaked at 400° C. forone hour in the case of the polyimide or at greater than 300° C. for theresist.

[0177] The dielectric layer 232 is plasma etched down to the sacrificiallayer 228 taking care not to remove any of the sacrificial layer 234.

[0178] This step defines the nozzle opening 124, the lever arm 126 andthe anchor 154 of the nozzle arrangement 110.

[0179] A high Young's modulus dielectric layer 238 is deposited. Thislayer 238 is formed by depositing 0.2 μm of silicon nitride or aluminumnitride at a temperature below the hardbaked temperature of thesacrificial layers 208, 212, 220 and 228.

[0180] Then, as shown in FIG. 37p of the drawings, the layer 238 isanisotropically plasma etched to a depth of 0.35 microns. This etch isintended to clear the dielectric from the entire surface except the sidewalls of the dielectric layer 232 and the sacrificial layer 234. Thisstep creates the nozzle rim 136 around the nozzle opening 124, which“pins” the meniscus of ink, as described above.

[0181] An ultraviolet (UV) release tape 240 is applied. 4 μm of resistis spun on to a rear of the silicon wafer 116. The wafer 116 is exposedto mask 242 to back etch the wafer 116 to define the ink inlet channel148. The resist is then stripped from the wafer 116.

[0182] A further UV release tape (not shown) is applied to a rear of thewafer 16 and the tape 240 is removed. The sacrificial layers 208, 212,220, 228 and 234 are stripped in oxygen plasma to provide the finalnozzle arrangement 110 as shown in FIGS. 37r and 38 r of the drawings.For ease of reference, the reference numerals illustrated in these twodrawings are the same as those in FIG. 30 of the drawings to indicatethe relevant parts of the nozzle arrangement 110. FIGS. 40 and 41 showthe operation of the nozzle arrangement 110, manufactured in accordancewith the process described above with reference to FIGS. 37 and 38, andthese figures correspond to FIGS. 31 to 33 of the drawings.

[0183] It would be appreciated by a person skilled in the art thatnumerous variations and/or modifications may be made to the presentinvention as shown in the specific embodiments without departing fromthe spirit or scope of the invention as broadly described. The presentembodiments are, therefore, to be considered in all respects to beillustrative and not restrictive.

[0184] The presently disclosed ink jet printing technology ispotentially suited to a wide range of printing system including: colorand monochrome office printers, short run digital printers, high speeddigital printers, offset press supplemental printers, low cost scanningprinters high speed pagewidth printers, notebook computers with inbuiltpagewidth printers, portable color and monochrome printers, color andmonochrome copiers, color and monochrome facsimile machines, combinedprinter, facsimile and copying machines, label printers, large formatplotters, photograph copiers, printers for digital photographic“minilabs”, video printers, PHOTO CD (PHOTO CD is a registered trademark of the Eastman Kodak Company) printers, portable printers for PDAs,wallpaper printers, indoor sign printers, billboard printers, fabricprinters, camera printers and fault tolerant commercial printer arrays.

We claim:
 1. A method of fabricating a printhead chip for an inkjetprinthead, the printhead chip including a wafer substrate thatincorporates drive circuitry and defines a plurality of ink inletchannels, a plurality of nozzle arrangements positioned on thesubstrate, each nozzle arrangement including nozzle chamber walls thatdefine a nozzle chamber and an ink ejection port in fluid communicationwith the nozzle chamber with an ink inlet channel opening into thenozzle chamber and an actuator that is positioned in the nozzle chamber,the actuator having an electrical circuit connected to the drivecircuitry layer and positioned in thermal expansion material so that theexpansion material experiences thermal expansion when the heatingcircuit receives an electrical signal from the drive circuitry layer andthe actuator is displaced towards the ink ejection port to eject a dropof ink from the nozzle chamber, the method comprising the steps of:forming a layer of sacrificial material on the substrate, such that thelayer is between one and ten microns thick; forming a first layer of thethermal expansion material on the sacrificial material; forming theheater circuit on the first layer of thermal expansion material, thesacrificial material and the first layer of thermal expansion materialbeing formed to permit the electrical circuit to make electrical contactwith the drive circuitry; forming a second layer of the thermalexpansion material on the heater circuit; and removing the sacrificialmaterial.
 2. A method as claimed in claim 1, in which the layer ofsacrificial material is formed to be between three and six micronsthick.
 3. A method as claimed in claim 1, in which the thermal expansionmaterial and the heater circuit are formed so that each actuatoroverlies a respective ink inlet opening.
 4. A method as claimed in claim1, in which the expansion material is polytetrafluoroethylene (PTFE) andwhich includes the step of plasma processing the surface of the secondlayer of PTFE to render said surface hydrophilic.
 5. A method as claimedin claim 1, which includes the steps of forming a further layer ofsacrificial material on the second layer of PTFE, forming the nozzlechamber walls on the second layer of sacrificial material such that thenozzle chamber walls define the nozzle chamber and the ink ejection portin fluid communication with the nozzle chamber and removing the secondlayer of sacrificial material.
 6. A method as claimed in claim 1 whichincludes the step of forming the first and second layers of expansionmaterial and the heater circuit such that the actuator is a laminatedstructure with the heater circuit sandwiched between the first andsecond layers of expansion material.